Prime Minister Stephen Harper does not intend to testify in the trial of suspended senator Mike Duffy because he doesn’t have any useful information to offer, his office said Tuesday.

RCMP laid 31 criminal charges against Duffy last week related to his disputed expenses, and experts say it’s likely that Harper could be called to testify in relation to the bribery charges Duffy faces, although he could invoke parliamentary privilege to avoid the witness box.

On Tuesday his director of communications, Jason MacDonald, said in an email that Harper doesn’t have helpful information.

“We have responded fully and freely to every request for assistance from the RCMP,” he said. “The RCMP have noted this and, after a thorough investigation, have made it clear who they believe is guilty of wrongdoing: Mike Duffy. They have also made clear that they do not believe the Prime Minister had any knowledge of Mr. Duffy’s wrongdoing. Given this, it is difficult to imagine that the Prime Minister would have any information that could be relevant to Mr. Duffy’s defence.”

If Harper is called to testify, he might be able to avoid it, but even trying to do so could open difficult legal and political questions, says former parliamentary law clerk Rob Walsh.

Among the charges the RCMP laid week are three bribery charges related to a $90,000 cheque he received from Nigel Wright, former chief of staff to the prime minister. Wright was not charged but is expected to testify.

Duffy, who says he is looking forward to answering the charges in court, has his first court appearance Sept. 16, the same day Harper and other MPs return to the House.

Harper’s work in the House means that he might not have to answer a subpoena because of the ancient principle of parliamentary privilege, which prevents members of Parliament from being dragged into court instead of attending to the nation’s business.

But two of the charges related to the $90,000 cheque — sections 119 and 122 of the Criminal code — might require the prime minister’s testimony, because what he knew about the payment could be relevant.

“If those are still in play, I would think Duffy could get out of those for lack of testimony from Harper,” said Walsh.

Walsh speculated that those charges could be dropped before the case goes to trial.

If they aren’t dropped, though, Harper would likely be asked to testify.

“If that’s the charge going forward, will he be called?” he said. “I think it’s likely one side or the other will call him. If he gets called, will he invoke privilege? That’s a tough one. He might like to, but he may decide the political cost is too high, depending on his circumstances at the time. Is he prime minister or not?”

In civil matters, there is a long-standing precedent that allows MPs to avoid testifying during a parliamentary session, or 40 days before or after such a session.

A parliamentary session ends when a prime minister asks the governor general to call an election or to prorogue, resetting the legislative agenda.

Prime Minister Stephen Harper speaks to the media in his office in Ottawa, Thursday June 26, 2014. THE CANADIAN PRESS/Adrian Wyld

Duffy has said he would like the trial to begin in early 2015, but it might take longer than that to get started, which means that, theoretically, it could be ongoing when we go to the polls in October. That would set up a scenario where Harper has to testify within days of the next election.

In practice, when an MP invokes privilege, it means it is impossible for them to testify.

Former Industry minister John Manley was able to avoid giving evidence for years in a case brought by a telecommunications company suing the government over a cellphone licence.

But Walsh is not sure how the law would apply to a criminal trial.

“The general rule is when a member is charged with a criminal offence, he cannot invoke privilege to avoid facing the charges,” he said. “The question is then, does that rule — exempting criminal proceedings from parliamentary privilege — apply to a subpoena issued in a criminal proceeding? I’m not sure on that. I don’t know of any case where that happened. Typically, in a criminal matter, a member of parliament wouldn’t invoke privilege, he’d just show up. So it’s never came to an issue.”

If Harper is subpoenaed, he could try to invoke privilege.

“He could make his case,” said Walsh. “Maybe the trial judge won’t accept it. If he succeeds, Duffy’s got the argument that he’s denied a fair trial because he doesn’t have the testimony of a key witness. That could put the court in a difficult position.”

Harper, who often declines to answer factual questions put to him by NDP Leader Tom Mulcair in the House, likely wouldn’t want to be cross examined in court, said Walsh.